Another "boiling" expansion tank story

[nomadros]

Truck: Mitsubishi Shogun Sport 2006
Got a problem which started yesterday. Arrived at my farm gate and I could hear a "bubbling" from the engine compartment, so had a look. The overflow from the expansion tank was overflowing and both the tank and radiator were making "bubbling" noises. Dash temp was normal.
Added coolant in the expansion tank this morning and did a test run. Truck was fine for about 35kms until I got to a long hill, started going up and after a few hundred metres, I could hear the "bubbling" noise. Kept going for about 6kms (it's a long slope with steep and nearly flat sections) before stopping.

Been running the engine whilst stationary for a bit now and no "bubbling". Electric fan works, dash temp normal, oil clean. If I squeeze the top rad hose with the rad cap locked, I can push fluid into the expansion tank and with the rad cap unscrewed, no fluid movement, so the rad cap seems ok. Tried with heater blasting or aircon full on, with no problems.

So all I know is everything works fine until the engine is under load to climb a hill. Truck goes fine otherwise (no smoke of any colour), so I'm baffled. Any ideas anyone?

This truck has a hard life as a farm truck and I try to keep a preventative maintenance plan going for it. It passed its annual inspection a few days ago.

TIA

 

[JTK]

Bad radiator cap not holding pressure perhaps?

When the system is under a slight pressure, the boiling point is higher.

 

[MParr]

Head gasket?

 

[Lubener]

I would connect a scan tool to see the actual coolant temperature being seen by the computer.

 

[Warstud]

If you had to add coolant....then that was part of the problem. Now going up hill the truck has to work harder and gets less airflow. So either the radiator needs cleaning or replacing or the water pump is worn out. Try cleaning the radiator.

 

[JohnnyG]

Rev it up in park while watching the lower radiator hose. I've seen them get soft and suck in under load.

 

[HankHill]

Start with the simplest.

Check for cooling fan operation, If mechanical check the thermostat for play. Get someone to speed the engine and check fan operation again. If electrical test fans for operation. Find out if they're dual speeds, etc. Use a scanner and check the CTS operation.

Look for obstructions in the radiator cooling airflow. Nests mud etc. Check radiator for possible blockages, temperature dead spots, hose restrictions. Look for information of common hose collapsing issues, etc

Replace the thermostat

Water pump failing, internal structure ie impeller. take the belt off and check

Head gasket issue, leak down or chemical testing

Look for information of common hose collapsing issues, etc

Thats all I have..

My next step would be to pull the pump and check its condition..

 

[mk378]

If I squeeze the top rad hose with the rad cap locked, I can push fluid into the expansion tank

That is bad. The cap should not let coolant out of the radiator until the rated pressure is reached. When the system can't build pressure, the coolant will boil at a lower temperature.

There is a check valve in the cap to let coolant back in to the radiator at low pressure as the engine cools after shutdown.

 

[HankHill]

That is bad. The cap should not let coolant out of the radiator until the rated pressure is reached. When the system can't build pressure, the coolant will boil at a lower temperature.

There is a check valve in the cap to let coolant back in to the radiator at low pressure as the engine cools after shutdown.

Oh crap I missed that part! Yeah, that's a sure sign....

 

[billt460]

Bad radiator cap not holding pressure perhaps?

When the system is under a slight pressure, the boiling point is higher.

I had that happen to a older Buick Century I had. It was a bad radiator cap. Put on a new one and the problem disappeared.

 

[nomadros]

Thanks for all the replies. The truck is outside the mechanics cooling down so we can have a good look. Hoping for a radiator cap fix but expecting a water pump fix.

 

[Snagglefoot]

Use a lazar pointed infra red temp gun to confirm temps. Most coolant containers are pressure sealed and if your coolant is near 212 F and there is a leak it may boil. Also check your antifreeze concentration. The higher the concentration, the higher the boiling point.

 

[nomadros]

Thanks... All coolant here (Spain) is sold premixed at 30%. I've checked for nests and mud. I have to do that every week due to nests and mud! I'm forever soldering cables back together after another mousefest. Anyway, once the water has cooled we'll go through everything step by step. Let's hope it's the rad cap.

 

[Marcozi]

Use a lazar pointed infra red temp gun to confirm temps. Most coolant containers are pressure sealed and if your coolant is near 212 F and there is a leak it may boil. Also check your antifreeze concentration. The higher the concentration, the higher the boiling point.

Actually, the higher the antifreeze content the lower the boiling point.

 

[billt460]

Actually, the higher the antifreeze content the lower the boiling point.

https://seeburgservicecenter.com/how-does-antifreeze-work

"Pure water, as you may know, has a boiling point of 212°F (100°C) and a freezing point of 32°F (0°C). However, when you create a 50/50 mixture using water and ethylene glycol, the boiling point rises to 223°F (106°C) and the freezing point lowers to -35°F (-37°C). When you take it one step further, creating a 30/70 mixture of water and ethylene glycol, the boiling point rises to 235°F (113°C) and the freezing point lowers to -67°F (-55°C).

 

[nomadros]

Anyhoo... we started the engine from cold, brought it up to temperature, switched on about everything we could and simulated a drive at 3000rpm for about 30 minutes. Result was...

Everything worked fine.

Then I drove the thing 5kms up a hill and the problem returned. Expansion tank full and overflowing.

So standing still, where the temp is 33c in the shade, with engine roaring for 30 mins and everything works.

12 min drive up a hill and end o' the world.

Tomorrow morning I have to get up early to spray crops, after that I'll take it back to the mechanic and we'll order parts (thermostat, hoses, rad cap, the easy stuff) and clean everything out. If that doesn't fix this then we're left with the expensive options.

Need beer.

 

[JohnnyG]

Actually, the higher the antifreeze content the lower the boiling point.

Show me that chart please.

 

[kschachn]

Show me that chart please.

Here is the correct chart. That poster has a history of posting nonsense.

 

[JohnnyG]

Here is the correct chart. That poster has a history of posting nonsense.

View attachment 102146

Hmm, Something is ASKEW!

 

[JohnnyG]

Maybe he was thinking about the FREEZING point. I remember an old wives tale that said that pure antifreeze will freeze before straight water would.
Of course, I know that's also nonsense, but some people firmly believed it.